It's no wonder Warren Buffett loves bank stocks.

The legendary billionaire investor has more than 30% of his $170 billion portfolio at Berkshire Hathaway (NYSE: BRK-A) (NYSE: BRK.B) dedicated to this one industry.

The reason why is simple: Bank stocks possess many of the important Buffett must-haves to be considered for his portfolio. First, banking institutions serve an important societal need that will never go away. Second, banking business models are relatively simple to understand, a key requirement of Buffett's investing philosophy. Third, despite the health of many banks improving dramatically since the 2008 financial crisis, some bank stocks are still trading at a bargain -- a key indicator that now is the best time to invest.

Read more at The Motley Fool.